Flow sensor with hot film anemometer

ABSTRACT

A method for determining flow velocity in a flow path, comprises defining a flow path for a fluid, the fluid flowing in a downstream direction that is opposite an upstream direction. A thermally-conductive element is exposed to the flow path. A known amount of heat is applied to a first portion of the thermally-conductive element and a sensed temperature is sensed at a second portion of the thermally-conductive element downstream of the first portion. The known amount of heat and the sensed temperature are used to determine a flow velocity of the fluid in the flow path.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/466,517 filed Mar. 22, 2017.

BACKGROUND

The present invention relates to a flow sensor, and more particularly toa flow sensor including a tube and separately-formed base that isinstallable in a window in the tube and connectable to a hot filmanemometer sensor.

SUMMARY

In one aspect, the invention provides a method for determining flowvelocity in a flow path, comprising: defining a flow path for a fluid,the fluid flowing in a downstream direction that is opposite an upstreamdirection; exposing a thermally-conductive element to the flow path;applying a known amount of heat to a first portion of thethermally-conductive element; sensing a sensed temperature of a secondportion of the thermally-conductive element downstream of the firstportion; and determining a flow velocity of the fluid in the flow pathbased on the known amount of heat and the sensed temperature.

In another aspect, defining a flow path for a fluid comprises providinga tube having a tube wall surrounding the flow path and having alongitudinal axis extending in the downstream direction. In anotheraspect, exposing a thermally-conductive element to the flow pathcomprises defining a window in the tube wall and positioning thethermally-conductive element in the window with a side of thethermally-conductive element facing the flow path. In another aspect,positioning the thermally-conductive element in the window includesrecessing the thermally-conductive element in the tube wall. In anotheraspect, the invention further comprises sealing the thermally-conductiveelement in the window to prevent fluid in the flow path from leaking outof the window. In another aspect, exposing a thermally-conductiveelement includes providing a piece of thermally-conductive materialhaving a thickness no greater than 0.004 inch and exposing a firstsurface of the piece of thermally-conductive material to the flow path.In another aspect, exposing a thermally-conductive element includesproviding a piece of thermally-conductive material having a firstsurface facing toward the fluid flowing in a downstream direction and asecond surface facing away from the fluid flowing in a downstreamdirection; applying a known amount of heat includes applying the knownamount of heat to the second surface; and sensing a sensed temperatureincludes sensing a temperature of the second surface. In another aspect,sensing a sensed temperature further includes mounting a temperaturesensor to a sensor-mounting section of the second surface for sensingthe temperature of the second surface. In another aspect, providing apiece of thermally-conductive material includes making the first andsecond surfaces of the thermally-conductive element planar and parallelto each other in the sensor-mounting section. In another aspect,applying a known amount of heat and sensing a sensed temperature, anddetermining a flow velocity are all done under the control of thecontroller. In another aspect, the invention further comprises providinga hot film anemometer flow sensor having a heater and a temperaturesensor; wherein applying a known amount of heat is performed with theheater; and sensing a sensed temperature is performed with thetemperature sensor.

Other aspects of the invention will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of a flow sensor accordingto the present invention.

FIG. 2 is an exploded view of the flow sensor.

FIG. 3 is a cross-section view of the sensor taken along line 3-3 inFIG. 1.

FIG. 4 is a cross-section view of the sensor taken along line 4-4 inFIG. 1.

FIG. 5 is a perspective view of a tube of the flow sensor.

FIG. 6 is a side view of the tube.

FIG. 7 is a perspective view of a base portion of the flow sensor andportions of the hot film anemometer sensor.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways.

FIGS. 1-4 illustrate a flow sensor assembly 100 that can be used, forexample, with a water treatment unit to determine flow velocities andrates at an inlet and outlet. The flow sensor assembly 100 includes atube 110, a base 120, hot film anemometer 130, a sealing assembly 140,and a mounting assembly 150.

With additional reference to FIGS. 5-6, the tube 110 is an elongatedmember having a tube wall 210 and an internal flow path 220 defining alongitudinal axis 230. For reference elements, directions, anddimensions generally perpendicular to the longitudinal axis 230 arereferred to with the terms “side,” “sides,” and “width” and thoseparallel to the longitudinal axis 230 are referred to with the term“end,” “ends,” and “length.” The tube wall 210 and flow path 220 aregenerally cylindrical or circular in a cross-section perpendicular tothe longitudinal axis 230, such as FIG. 4.

The tube 110 includes a longitudinally-extending window 240 in the tubewall 210 and a pair of flanges 250 on opposite sides of the window 240.The window 240 includes a frame 260 recessed in the tube wall 210 and anopening 270 surrounded by the frame 260. The opening 270 communicateswith the flow path 220. The frame 260 includes relatively planar, thinside portions 280 along the sides of the opening 270 and ramped endportions 290 at the opposite ends of the opening 270. The ramped endportions 290 angle upwardly from the ends of the opening 270 to theouter surface of the tube 110. As illustrated in FIG. 3, the angle α ofthe ramped end portions 290 with respect to the longitudinal axis 230 isabout 22 degrees as illustrated, any angle in the range of 12-32 degreesshould be suitable for this application. Formed into the side portions280 and ramped end portions 290 of the frame 260 is a continuous seat295 for use with the sealing assembly 140 as will be described in moredetail below.

Referring now to FIG. 7, the base 120 is a very thin (e.g., no thickerthan about 0.004 inch) piece of thermally-conductive material such assteel and is received in the window 240. The base 120 extends in thelongitudinal direction. A surface of the base 120 facing toward the flowpath 220 is referred to as the inwardly-facing surface 330 and theopposite surface (facing away from the flow path 220) is referred to asthe outwardly-facing surface 340. The thickness of the base 120 is areference to the distance between the inwardly-facing surface 330 andoutwardly-facing surface 340. The base 120 includes a central section350 and an angled end section 360 at each end of the central section350. The central section 350 and the angled end sections 360 are allflat or planar, with the angled end sections 360 extend at the angle αwith respect to the central section 350 (i.e., at about the same angle αof the ramped end portions 290). The inwardly-facing surface 330 andoutwardly-facing surface 340 are parallel to each other in each section350, 360.

The base 120 includes a periphery or perimeter 370 extending over theframe 260 of the window 240, with the perimeter 370 of the centralsection 350 being supported by the side portions 280 of the frame 260and the perimeter 370 of the angled end sections 360 being supported bythe ramped end portions 290 of the frame 260. The central section 350 ofthe base 120 covers the opening 270 of the window 240, with theinwardly-facing surface 330 being exposed to (i.e., in direct contactwith) fluid in the flow path 220. Referring to FIG. 4, the centralsection 350 truncates the circular cross-section of the flow path 220and appears as a chord in the transverse cross-section view. The centralsection 350 may also be referred to as the sensor-mounting sectionbecause components of the hot film anemometer 130 are mounted to it.

With reference to FIGS. 1-4 and 7, the hot film anemometer 130 includesa heater 420, a sensor 430, a controller 440, and wires 450 connectingthe controller 440 to the heater 420 and sensor 430. The heater 420 andsensor 430 are secured to the central section 350 of the base 120through thermally-conductive means such as precision soldering orbrazing that minimizes or eliminates air pockets or any other thermalinsulators. The heater 420 is upstream from the sensor 430 in thelongitudinal direction with respect to an expected flow direction 460(FIG. 3) of fluid in the flow path 220. The heater 420 generates aprecise amount of heat, as determined by the controller 440, The heat ispassed to the fluid in the flow path 220 by conduction through thecentral section 350 of the base 120. The sensor 430 senses thetemperature of the fluid in the flow path 220 by conduction through thebase 120, and provides the temperature information to the controller440. The controller 440 calculates fluid flow velocity as a function ofthe heat generated by the heater 420, the heat sensed by the sensor 430,the distance between the heater 420 and the sensor 430, the thermalconductivity and thickness of the base 120, the properties of fluid inthe flow path 220, and other factors. The controller 440 may alsocalculate the flow rate of the fluid if the dimensions of the flow path220 are provided. Controller 440 communicates with the heater 420 andsensor 430 through wires 450 in the illustrated embodiment, but in otherembodiments could use wireless communication.

Referring primarily to FIG. 2, the sealing assembly 140 includes a seal520 (e.g., a gasket, an O-ring, or other type of seal), a clamping block530, and a clamping plate 540. The seal 520 is positioned in the seat295 in the frame 260 and thus surrounds the opening 270. The clampingblock 530 includes a central portion 550 and ramped end portions 560that substantially follow the shape of the outwardly-facing surface 340of the central section 350 and angled end sections 360 of the base 120.The clamping block 530 and clamping plate 540 include alignedpass-through holes 570, 580, respectively, through which the wires 450of the hot film anemometer 130 extend.

During assembly, the base 120 is positioned in the window 240 with itsperimeter 370 in contact with the seal 520 and the clamping block 530 isinserted into the window 240 on top of the base 120 with the wires 450extending through the pass-through holes 570 in the clamping block 530.Then the clamping plate 540 is mounted with fasteners to the flanges 250on the tube 110, with the wires 450 extending through the pass-throughholes 580. The flanges 250, clamping block 530, and clamping plate 540are sized and configured such that the clamping plate 540 contacts thetop of the clamping block 530 when the clamping plate 540 is secured tothe flanges 250. The clamping plate 540 applies a radially-directed(i.e., generally toward the longitudinal axis 230) clamping force to theclamping block 530, which clamps the base 120 against the frame 260. Theseal 520 is sandwiched between the perimeter 370 of the base 120 and theframe 260 to create a water-tight seal between the base 120 and the tube110. Depending on how it is configured and the requirements of thespecific application, the water-tight seal may be rated up to 100 psi,200 psi, 300 psi, or 400 psi. The water-tight seal resists leakage offluid from the flow path 220 through the window 240.

The mounting assembly 150 may include a mounting plate 620 that issecured to a side of the clamping plate 540 with fasteners.Alternatively, the mounting plate 620 may be formed integrally with theclamping plate 540. The mounting plate 620 may be secured to aconvenient mounting place in the environment in which the flow sensorassembly 100 is used.

It should be noted that the base 120 can be formed relatively easilyfrom thin sheet material that can be formed in a relatively simplesingle or multiple step forming process. The window 240 can be includedin the formation process of the tube 110 (e.g., injection molding). Thepresent invention therefor provides a method of manufacturing thatincludes separately producing the base 120 and tube 110 with relativelysimple yet reliable processes and later install the base 120 into thewindow 240. This is advantageous compared to machining, modifying, orotherwise post-processing a portion of a tube wall made of athermally-conductive material to provide a sensor-mounting section thatis integrally formed with the thermally-conductive tube wall. Suchpost-processing of the tube wall can be time-consuming, complicated, andless reliable than the present invention, especially when a very thin,planar sensor-mounting section is necessary or desirable. The presentinvention is also advantageous because the same base 120 and sealingassembly 140 can be used on tubes 110 of different sizes, provided thatthe window 240 formed in the tubes 110 is consistently sized.

Thus, the invention provides, among other things, a flow sensor mountedin a window provided in a tube wall, such that the sensor is exposed tothe fluid flowing through flow path in the tube. Various features andadvantages of the invention are set forth in the following claims.

What is claimed is:
 1. A method for determining flow velocity in a flowpath, comprising: defining a flow path for a fluid, the fluid flowing ina downstream direction that is opposite an upstream direction; exposinga thermally-conductive element to the flow path; applying a known amountof heat to a first portion of the thermally-conductive element; sensinga sensed temperature of a second portion of the thermally-conductiveelement downstream of the first portion; and determining a flow velocityof the fluid in the flow path based on the known amount of heat and thesensed temperature.
 2. The method of claim 1, wherein defining a flowpath for a fluid comprises providing a tube having a tube wallsurrounding the flow path and having a longitudinal axis extending inthe downstream direction.
 3. The method of claim 2, wherein exposing athermally-conductive element to the flow path comprises defining awindow in the tube wall and positioning the thermally-conductive elementin the window with a side of the thermally-conductive element facing theflow path.
 4. The method of claim 3, wherein positioning thethermally-conductive element in the window includes recessing thethermally-conductive element in the tube wall.
 5. The method of claim 3,further comprising sealing the thermally-conductive element in thewindow to prevent fluid in the flow path from leaking out of the window.6. The method of claim 1, wherein exposing a thermally-conductiveelement includes providing a piece of thermally-conductive materialhaving a thickness no greater than 0.004 inch and exposing a firstsurface of the piece of thermally-conductive material to the flow path.7. The method of claim 1, wherein: exposing a thermally-conductiveelement includes providing a piece of thermally-conductive materialhaving a first surface facing toward the fluid flowing in a downstreamdirection and a second surface facing away from the fluid flowing in adownstream direction; applying a known amount of heat includes applyingthe known amount of heat to the second surface; and sensing a sensedtemperature includes sensing a temperature of the second surface.
 8. Themethod of claim 7, wherein sensing a sensed temperature further includesmounting a temperature sensor to a sensor-mounting section of the secondsurface for sensing the temperature of the second surface.
 9. The methodof claim 8, wherein providing a piece of thermally-conductive materialincludes making the first and second surfaces of thethermally-conductive element planar and parallel to each other in thesensor-mounting section.
 10. The method of claim 1, wherein applying aknown amount of heat and sensing a sensed temperature, and determining aflow velocity are all done under the control of the controller.
 11. Themethod of claim 1, further comprising providing a hot film anemometerflow sensor having a heater and a temperature sensor; wherein applying aknown amount of heat is performed with the heater; and sensing a sensedtemperature is performed with the temperature sensor.